It is known to provide a motor vehicle with a fuel supply system having a high pressure fuel pump to supply fuel at high pressure such as 200 MPa to one or more fuel injectors of an engine such as, for example, a diesel engine or gasoline direct injection engine. It is a problem with prior fuel supply systems that the quantity of fuel supplied by the fuel pump when the fuel pump is operating at peak efficiency does not always match the fuel requirements of the engine to which fuel is supplied. In FIG. 7 a fuel quantity versus engine speed chart is shown for a typical high pressure fuel pump in which two exemplary situations of this problem are indicated.
For example, in FIG. 7 the lines x1 to x6 are lines joining points of equal high pressure fuel pump efficiency, the broken line ‘Of’ is a line joining points of optimum fuel pump efficiency throughout the operating speed range of the engine, Max Eff is an operational point where the high pressure fuel pump is operating at a maximum or peak efficiency and Fd max is a line showing the maximum possible fuel demand for the engine throughout its operating speed range.
In situation “A” the supply of fuel required for the engine is more than the high pressure fuel pump can supply when operating at optimum efficiency for that engine speed. Therefore in such a situation the high pressure fuel pump needs to be operated with an output greater than is optimal for that engine speed in order to meet the fuel demand from the engine. This requires the high pressure fuel pump to be operated at an operating efficiency less than optimal thereby wasting energy driving the high pressure fuel pump.
In situation “B” the high pressure fuel pump is capable of supplying more fuel to the engine than is required to fuel the engine. In such a case either the output from the high pressure fuel pump has to be reduced or excess fuel has to be returned to a low pressure reservoir. In either case energy is wasted either by operating the high pressure fuel pump below its optimum efficiency or by operating at optimum efficiency but producing more fuel than is required.
The inventors have recognized issues with the approaches above and herein provide a method and system for reducing the fuel usage of an engine by operating a high pressure fuel pump more efficiently. According to a first aspect of the present disclosure there is provided a method of controlling an engine fuel supply system comprising an engine driven high pressure fuel pump, a valve means and a high pressure accumulator wherein the method comprises, operating the high pressure fuel pump at one of a zero demand level and an optimum demand level while using the valve to control the flow of fuel to the engine from the high pressure fuel pump and the accumulator to meet a fuel demand from the engine unless the accumulator is empty and the fuel demand from the engine is greater than the amount of fuel available from the high pressure fuel pump when operated at the optimum demand level. In this way, the accumulator may be selectively connectable to the high pressure fuel pump and the engine such that it is connected during some conditions, and not connected during other conditions.
Furthermore, the technical result is achieved that the high pressure fuel pump is operated as efficiently as possible for the maximum time possible.
The method may further comprise determining a current fuel level in the high pressure accumulator, the fuel demand from the engine and a current fuel quantity available from the high pressure fuel pump when operating at the optimum demand level and controlling the flow of fuel to the engine from the high pressure fuel pump and the accumulator to meet the fuel demand from the engine based upon at least one of the amount of fuel stored in the accumulator and a comparison of the current fuel quantity available from the high pressure fuel pump when operating at the optimum demand level with the fuel demand from the engine.
Therefore the flow of fuel to the engine from the high pressure fuel pump and the accumulator may be controlled to meet the fuel demand from the engine based upon at least one of the amount of fuel stored in the accumulator and a comparison of the current optimum fuel quantity available from the high pressure pump with the fuel demand from the engine in order to minimize running of the high pressure fuel pump above a fuel demand level where the optimum fuel quantity is available from the high pressure fuel pump.
If an amount of fuel greater than a predetermined amount is present in the high pressure accumulator then the method may comprise using the fuel from the accumulator and operating the high pressure at a zero demand level. Alternatively, if the amount of fuel in the accumulator is below a predefined threshold and the fuel demand from the engine is less than the current fuel quantity available from the high pressure fuel pump when operating at the optimum demand level, the high pressure fuel pump may be operated at the optimum fuel demand level and any excess fuel is supplied from the high pressure fuel pump to the high pressure accumulator. Still further, if the amount of fuel in the accumulator is below a predefined threshold and the fuel demand from the engine is equal to the current fuel supply output available from the high pressure fuel pump when operating at the optimum demand level, the high pressure fuel pump may be operated at the optimum demand level to supply fuel to the engine. The predefined threshold may be one of a lower predefined threshold and an upper predefined threshold.
If the amount of fuel in the accumulator is empty and the fuel demand from the engine is more than the current fuel quantity available from the high pressure fuel pump when operating at the optimum demand level, the high pressure fuel pump may be operated at a demand level required to meet the fuel demand from the engine. The accumulator may be empty if the amount of fuel in the accumulator is below a predefined lower threshold.
If the amount of fuel in the accumulator is above a predefined upper threshold, the high pressure fuel pump may be operated at a zero demand level and fuel may be supplied to the engine from the high pressure accumulator to meet the fuel demand from the engine. The level of fuel in the high pressure accumulator may be determined by measuring the pressure of the fuel stored in the high pressure accumulator. The predefined lower threshold may be a predefined lower pressure threshold. The predefined upper threshold may be a predefined upper pressure threshold.
If the amount of fuel in the accumulator is between a predefined lower threshold and a predefined upper threshold and the fuel demand from the engine is more than the current fuel quantity available from the high pressure fuel pump when operating at the optimum demand level, the high pressure fuel pump is operated at a zero demand level and fuel is supplied to the engine from the high pressure accumulator to meet the fuel demand from the engine.
If the amount of fuel in the accumulator is between a predefined lower threshold and a predefined upper threshold and the fuel demand from the engine is one of more than and equal to the current fuel quantity available from the high pressure fuel pump when operating at the optimum demand level, the high pressure fuel pump is operated at a zero demand level and fuel is supplied to the engine from the high pressure accumulator to meet the fuel demand from the engine.
According to a second aspect of the present disclosure there is provided an engine fuel supply system comprising a fuel reservoir, a low pressure fuel pump to supply fuel from the reservoir to an engine driven high pressure fuel pump, at least one fuel injector to supply fuel at high pressure to the engine, a fuel accumulator to store fuel at high pressure, a valve means to control the flow of fuel between the high pressure fuel pump, the accumulator and the engine and an electronic controller to control the operation of the high pressure fuel pump, the valve means and the at least one fuel injector, wherein the electronic controller operates the high pressure fuel pump at one of a zero demand level and an optimum demand level and uses the valve to control the flow of fuel to the engine from the high pressure fuel pump and the accumulator to meet a fuel demand from the engine unless the accumulator is empty and the fuel demand from the engine is greater than the amount of fuel available from the high pressure fuel pump when operated at the optimum demand level. This has the advantage that the high pressure fuel pump is operated as efficiently as possible for the maximum time possible.
The electronic controller may be further operable to estimate a current fuel level in the high pressure accumulator, estimate the fuel demand from the engine and estimate a current fuel quantity available from the high pressure fuel pump when operating at the optimum demand level and control the flow of fuel to the engine from the high pressure fuel pump and the accumulator to meet the fuel demand from the engine based upon at least one of the amount of fuel stored in the accumulator and a comparison of the current fuel quantity available from the high pressure pump when operating at the optimum demand level with the fuel demand from the engine.
Therefore the flow of fuel to the engine from the high pressure fuel pump and the accumulator may be controlled by the electronic controller to meet the fuel demand from the engine based upon at least one of the amount of fuel stored in the accumulator and a comparison of the current optimum fuel quantity available from the high pressure pump with the fuel demand from the engine in order to minimize running of the high pressure fuel pump above a fuel demand level where the optimum fuel quantity is available from the high pressure fuel pump.
If the amount of fuel in the accumulator is below a predefined threshold and the fuel demand from the engine is less than the current fuel quantity available from the high pressure fuel pump when operating at the optimum demand level, the electronic controller operates the high pressure fuel pump at the optimum fuel demand level and controls the valve means so that any excess fuel is supplied from the high pressure fuel pump to the high pressure accumulator.
If the amount of fuel in the accumulator is below a predefined threshold and the fuel demand from the engine is equal to the current fuel quantity available from the high pressure fuel pump when operated at the optimum fuel demand level, the electronic controller may operate the high pressure fuel pump at the current optimum fuel demand level and may control the valve means to supply fuel to the engine. The predefined threshold may be one of a lower predefined threshold and an upper predefined threshold.
If the amount of fuel in the accumulator is empty and the fuel demand from the engine is more than that available if the high pressure fuel pump is operated at the optimum fuel demand level, the electronic controller may operate the high pressure fuel pump at a demand level required to meet the fuel demand from the engine and may operate the valve means to supply fuel from the high pressure fuel pump to the engine, to isolate the high pressure accumulator from the high pressure fuel pump and isolate the high pressure accumulator from the engine. The accumulator may be empty if the amount of fuel in the accumulator is below a predefined lower threshold.
If the amount of fuel in the accumulator is above a predefined threshold, the electronic controller operates the high pressure fuel pump at a zero demand level and operates the valve means to permit fuel to be supplied to the engine from the high pressure accumulator to meet the fuel demand from the engine.
If the amount of fuel in the accumulator is between a predefined lower threshold and a predefined upper threshold and the fuel demand from the engine is more than the current fuel quantity available from the high pressure fuel pump when operating at the optimum demand level, the electronic controller operates the high pressure fuel pump at a zero demand level and operates the valve means to supply fuel from the high pressure accumulator to the engine to meet the fuel demand from the engine.
If the amount of fuel in the accumulator is between a predefined lower threshold and a predefined upper threshold and the fuel demand from the engine is one of more than and equal to the current fuel quantity available from the high pressure fuel pump when operating at the optimum demand level, the electronic controller operates the high pressure fuel pump at a zero demand level and operates the valve so that fuel is supplied to the engine from the high pressure accumulator to meet the fuel demand from the engine.
According to a third aspect of the present disclosure there is provided a motor vehicle having an engine and a fuel supply system wherein the fuel supply system is a fuel supply system constructed in accordance with said second aspect of the present disclosure.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description.
Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.